A nut kernel, the component of the nut that remains after shelling, is comprised of a nut meat that is covered by a brownish skin. Removal of the skin, a process called blanching, is desired for many varieties of nuts. For example, the skins of hazelnuts and Brazil nuts have unpleasant bitter tastes. For other nuts, such as almonds, removal of the skin is desired to prevent the brownish skin from coloring foods that are prepared using the nuts.
Certain nuts, such as hazelnuts and Brazil nuts, have a tightly adhering skin which is difficult to remove due to deeply embedded vein networks, The convoluted surfaces of these and other nuts, such as almonds, make it difficult to abrade the skins from the nuts without significant loss of nut meat. Often mechanical abrasion of these nuts results in a loss of 10 to 20% of the valuable nut meat.
Various other processes have been used for removing the skin from these types of nuts. These processes have enjoyed limited success. For the most part, existing processes are unsatisfactory because they do not completely remove the skin without abrading away significant amounts of nut meat or because they adversely affect the taste, appearance or shelf life of the nuts.
Some existing processes involve removing the skins by high pressure jets of water or by scalding water. Unfortunately, high water pressure also may erode areas of the nut meat and create pits in the surface of the nuts. Breakage is also known to occur. Further, nuts treated with these methods tend to absorb water and thus require drying, a process which weakens the flavor of the nuts by causing them to lose some of their oils. Almonds are commonly blanched by scalding, but this process also requires extended periods of drying and a resultant decrease in flavor.
In a common chemical process for removing skins from nut kernels, the nuts are first immersed in an alkaline bath, subsequently immersed in an acid bath, and finally subjected to mechanical abrasion. Alkaline solutions are believed to break down the oily component thought responsible for adhering the skin to the nut meat. Because alkaline solutions discolor the nut meats making them commercially undesirable, the subsequent acid bath is thus used to prevent discoloration. The acid leaves the nuts with an unpleasant bitter taste and may reduce their shelf life. Moreover, the concentrations of the chemical solutions dilute over the soaking period because of debris introduced into the solutions by the nuts. Dilution makes regulation of the concentration of the solutions highly difficult and renders these processes unfeasible for large scale blanching operations.
Hazelnuts are frequently blanched by roasting the nuts at approximately 350.degree. F. for 7 minutes and then mechanically abrading the skins from the nuts. Although this method is satisfactory at removing the nut skins, it produces nuts having a roasted flavor.